Fluid angular rate sensor

ABSTRACT

An improved fluid readout means for devices that measure the angular rate of rotation of a body about an axis. A slotted cylinder is positioned in the drain of a vortex rate sensor, with its axis transverse to the drain axis. The slots are located in the upstream portion of the cylinder and are at a very small radius from the drain axis. As the helical angle of the flow through the drain changes due to changes in rotation of the rate sensor the static pressure at the slots changes, and the pickoff produces a fluid output signal which is proportional to the angular rate of rotation of the sensor. Increased sensitivity may be achieved by introducing an airfoil section upstream of and in close proximity with the slotted cylinder. Alternatively, an airfoil section can be positioned to extend completely across the drain and serve to direct the helical flow to a splitter located downstream of the airfoil to produce a high flow output signal that is proportional to the angular rate of rotation of the sensor.

United States Patent [191 Scudder [111 E Re. 28,621

[ 5] Reissued Nov. 25, 1975 FLUID ANGULAR RATE SENSOR Kenneth R.Scudder, Chevy Chase, Md.

[22] Filed: July 17, 1969 [211 App]. No.: 852,265

Related U.S. Patent Documents [75] Inventor:

3,386,291 6/1968 Evans et al. 73/505 Primary Examiner-Herbert GoldsteinAttorney, Agent, or FirmNathan Edelberg; Robert P. Gibson; Saul Elbaum[57] ABSTRACT An improved fluid readout means for devices that measurethe angular rate of rotation of a body about an axis. A slotted cylinderis positioned in the drain of a vortex rate sensor, with its axistransverse to the drain axis. The slots are located in the upstreamportion of the cylinder and are at a very small radius from the drainaxis. As the helical angle of the flow through the drain changes due tochanges in rotation of the rate sensor the static pressure at the slotschanges, and the pickoff produces a fluid output signal which isproportional to the angular rate of rotation of the sensor. Increasedsensitivity may be achieved by introducing an airfoil section upstreamof and in close proximity with the slotted cylinder. Alternatively, anairfoil section can be positioned to extend completely across the drainand serve to direct the helical flow to a splitter located downstream ofthe airfoil to produce a high flow output signal that is proportional tothe angular rate of rotation of the sensor.

7 Claims, 11 Drawing Figures Reissued Nov. 25, 1975 Sheet 1 of2 Re.28,621

HTTDRNEYS Reissued Nov. 25, 1975 Sheet 2 of2 Re. 28,621

| I TRANSIT\ON L IZEG\ON 1 FLUID ANGULAR RATE SENSOR Matter enclosed inheavy brackets I: 1 appears in the original patent but forms no part ofthis reissue specification; matter printed in italics indicates theadditions made by reissue.

This invention relates to pure fluid devices for measuring the angularrate of rotation of a body about an axis and particularly to improvedfluid readout means for such devices.

The state-of-the-art of pure fluid devices has been considerablyadvanced since the basic fluid amplifiers were built and tested at theHarry Diamond Laboratories in 1959. One example of the extent to whichthe state-of-the-art has advanced can be seen in the October 1964 issueof Control Engineering, wherein an all fluid no-moving parts attitudecontrol system for a missile is described. This system is designed totake the error signals of an attitude sensing device and modulate andamplify these signals to ultimately control the attitude of the missile.Since the control system is designed to be all fluid-operated andwithout moving parts, the output from the attitude sensing device mustbe in the form of fluid signals in order for the sensor to be compatiblewith the rest of the system.

One type of pure fluid attitude sensor that has been used to supply theerror signals for the missile control system is the fluid-operatedrotation sensing device disclosed by Romald E. Bowles in his patentapplication Ser. No. 171,538, now US. Pat. No. 3,320,815, filed Feb. 6,1962, and assigned to the assignee in the instant application. TheBowles rotation sensor is commonly referred to in the art as a vortexrate sensor because it operates on the principles of vortex mtion.

The operation of a vortex rate sensor can be easily understood byconsidering a relatively flat cylindrical chamber having a relativelysmall central drain or output passage therein to which fluid underpressure such as air is supplied at or near the circumference of thechamber. The chamber is provided normally with an annular ring orcoupler made ofa porous materialsuch that fluid flowing through thecoupler will have only a radial component of velocity. When the ratesensor is rotated in a plane perpendicular to its axis, a tangentialcomponent of velocity is imposed on the fluid as it leaves the couplerwhereby vortex flow is produced in the chamber and helical flow isproduced in the drain. Because of the conservation of angular momentum,the tangential velocity of the flow and consequently the velocity of thefluid in the vortex increases as the fluid reaches the drain, therebyproviding an amplification factor for the sensor. By appropriatelysensing the flow parameters in the drain, particularly the changes inthe helical angle, the angular rate of the sensor can be determined.

H. D. Ogren in his recently issued US. Pat. No. 3,203,237 entitledVortex Rate Sensor, discloses a readout system for a vortex rate sensorcomprising a movable airfoil member connected to a transducing meanswhereby movement of the airfoil member in response to changes in thehelical flow in the drain will produce an electrical output signalindicative of the angular rate of rotation of the sensor. While Ogren'srate sensor has application to more conventional attitude controlsystems that utilize electrical error signals, his readout device wouldnot be useful in an all fluid control system such as contemplated above.

The Bowles rate sensor mentioned above provides the fluid readoutrequired by an all fluid attitude control or guidance system, butconsiderable difficulty has been encountered with the Bowles rate sensorin producing an output signal that has a high signal-to-noise ratio anda high sensitivity.

The instant invention is concerned with basically two types of fluidreadout means or pickoffs for a vortex rate sensor. The first type ofpickoff is employed when the device driven by the sensor has a highinput impedance and requires relatively low flow, and the second isemployed when the device driven by the sensor has a low input impedanceand requires relatively large flow.

At this point it would be useful to consider briefly the properties ofvortex sink flow, so that the invention can be more readily understood.

Vortex motion can be divided into two distinct types of motion, theforced vortex and the free vortex. The forced vortex occurs when allparticles of the fluid have the same angular velocity and, therefore,the tangential velocity, V,, is directly proportional to the radius.This is equivalent to solid body or wheel-like rotation and is sometimesreferred to as rotational flow. As the radius .increases, the tangentialvelocity increases linearly. In

lar momentum is assumed. When the total pressure isconsidered in avortex, it is seen that free vortex flow cannot occur in practice forvery small radii. For example, in the incompressible case V,=k/r where kis a constant.

Now P is a constant and P cannot in practice become negative; therefore,the tangential velocity, V cannot exceed the maximum velocity given byThe real vortex motion then has both forced vortex motion near its axisand free vortex motion 'at some distance from its axis. Separating thesetwo regions is a transition region where the tangential velocity reachesa maximum. This tangential velocity distribution is characteristic forall real vortex devices. The maximum tangential velocity, V occurs at asmall radius from the center which defines a circle called the limitcircle. For maximum sensitivity of the rate sensor; therefore, it isdesirable to position a pick-off in the vicinity of the limit circle sothat the maximum tangential velocity and consequently the maximumpressure change can be sensed.

It is, therefore, an object of the present invention to provide a vortexrate sensor having improved fluid readout means.

Another object of the instant invention is to provide a vortex ratesensor that produces fluid output signals having a high signal-to-noiseratio.

A further object of the instant invention. is to provide a vortex ratesensor that is sensitive throughout a wide range of changes in the flowdirection.

Still another object of the present invention is to provide a vortexrate sensor that produces fluid output signals for fluid devices whichhave high input impedances.

Yet another object of this invention is to provide a vortex rate sensorthat produces fluid output signals for fluid devices which have lowinput impedances.

In accordance with one aspect of the present invention, the foregoingand other objects are attained by providing pickoff means in the drainof a vortex rate sensor that comprises a slotted cylinder positionedwith its axis transverse to the drain axis wherein the slots are locatedin the upstream portion of the cylinder and are at a very small radiusfrom the drain axis. The slotted cylinder acts like a direction-findingpitot tube to measure the changes in the angle of the helical flowthrough the drain produced when the rate sensor is rotated in a planeperpendicular to its axis. As the helical angle changes, the staticpressure at the slots changes, and the pickoff produces a fluid outputsignal that is proportional to the angular rate of rotation of thesensor.

In accordance with another aspect of the invention, an airfoil sectionis positioned upstream of and in close proximity with a similarlypositioned slotted cylinder to amplify the change in helical angle ofthe flow through the drain as seen by the slotted cylinder.

In accordance with still another aspect of the instant invention anairfoil section is positioned to extend completely across the drain andserves to direct the helical flow to a splitter located downstream ofthe airfoil to produce a high flow output signal that is proportional tothe angular rate of rotation of the sensor.

The specific nature of the invention, as well as other objects, aspects,uses, and advantages thereof, will clearly appear from the followingdescription and from the accompanying drawings, in which:

FIG. 1 is a plan view, partly in section, of a vortex rate sensor;

FIG. 2 is a cross-sectional view taken along lines 2-2 of FIG. 1;

FIG. 3 is an enlarged cross-sectional view taken along lines 3-3 of FIG.2 and shows the positioning of a slotted cylinder pickoff in the draintube;

FIG. 4 is an enlarged cross-sectional view of the pickoff of FIG. 3taken along lines 4-4 of FIG. 3;

FIG. 5 is a prospective view of a slotted cylinder pickoff havingcircumferential slots;

FIG. 6 is a cross-sectional view of a portion of the drain tube of avortex rate sensor which shows an airfoil section in combination withthe slotted cylinder pickoff of FIG. 3;

FIG. 7 is an elevation partly in section taken along lines 7--7 of FIG.6;

FIG. 8 is a cross-sectional view showing a modified drain tube accordingto the instant invention which shows an airfoil section in combinationwith a splitter and multiple-flow output means;

FIG. 9 is a plan view, partly in section, taken along the lines 9-9 ofFIG. 8;

FIG. 10 is a plan view, partly in section, taken along the lines 10-10of FIG. 8; and

FIG. 11 is a graphical representation of the tangential velocitydistribution for the combined vortex sink flow.

Referring now to the drawing wherein like numerals designate identicalor corresponding parts throughout the several views, and moreparticularly to FIGS. 1 and 2 where there is shown a vortex rate sensorgenerally indicated by the reference numeral 10. Rate sensor 10 isessentially a relatively flat, hollow, cylindrical chamber that includesa circular top wall 11, a circular bottom wall 12 in spaced parallelrelation thereto, and an annular side wall 13 secured in a fluid tightrelation to the top and bottom walls by any suitable means such as thescrews 14. An annular porous ring or coupler 15 is positioned within thechamber of the rate sensor at a smaller radius than annular wall 13 andprovides a manifold 16 between coupler 15 and annular wall 13. Top andbottom walls 11 and 12, respectively, and annular wall 13 may beconstructed of any rigid material such as metal, glass, plastic or thelike that is compatible with and impervious to the working fluid.Coupler 15 is preferably made of a sintered metal but may be made of anysuitable porous material that allows fluid to pass through it with aminimum of restriction.

Fluid under pressure from a source (not shown) enters rate sensor 10 bymeans of one or more input nozzles 17 formed in the annular wall 13, andleaves the rate sensor by means of a centrally located drain tube 18provided in the bottom plate 12 to be discharged to the ambientcondition or to a sump (not shown). While only one drain is shown, itwill be obvious that a second drain may be provided in the top plate 11if desired.

Positioned within drain tube 18 is a fluid readout means 19 whichconsists essentially of a thin-walled cylindrical tube that extendsthrough the wall of the drain tube 18 and into the drain passage 21formed thereby to the central axis A-A. Readout means 19, referred toalso as a pickoff, senses changes in the fluid flow leaving the ratesensor 10 and transmits these changes as fluid output signals tosuitable fluid elements (not shown) in the rest of the control system ofwhich the rate sensor forms a part. In the missile guidance systemmentioned above, the fluid output signals from rate sensor 10 aretransmitted to the inputs of a fluid pulse width modulator such asdisclosed by Warren et a]. in their application Serial No. 3 12,808 nowUS. Pat. No. 3,228,4l0, filed Sept. 30, 1963, for Fluid Pulse WidthModulation." In another application, the fluid output signals producedby pickoff 19 might be amplified by means of a proportional fluidamplifier.

The details of pickoff 19 can be more readily appreciated with specificreference to FIGS. 3 and 4. Pickoff element 19 is preferably a slotted,hollow cylinder, closed at one end, which extends into the drain ofsensor 10 with its axis perpendicular to the drain axis which is alsothe sensor axis A-A. This pickoff element senses changes in the flowdirection in drain passage 21 in one embodiment by means of a pair ofparal lel arranged axial slots 22 and 23 which extend through thepickoff cylinder wall 24 and into a pair of separate output channels 25and 26, respectively, which are formed by a wall member 27. Theoperation of the slotted cylinder pickoff 19 can be explained byreferring to the two dimensional flow around a circular cylinder whoseaxis is perpendicular to the flow some distance ahead of the cylinder.The pressure distribution around such a cylinder is shown in FIG. 4 bythe distribution of the pressure difference, pp,,, somewhat asrepresented by the radial ordinates in FIG. 4, and by p+p/2(4V,, sinB)=H where H is the total pressure, p is the density, V is the fluidvelocity, p is the pressure at the angle 6, and 6 is the angle measuredfrom the stagnation point on the cylinder. At the stagnation point thepressure difference is When an aperture is provided in the surface ofthe cylinder, such as slots 22 and 23, at the critical angle 6, thepressure at this point is static. The slotted cylinder pickoff 19 can bepositioned with the slots at any desired 6. When the angle of thehelical flow through the drain passage 21 is changed, as by a change inthe angular rate of rotation of the sensor, the stagnation point on thecylinder shifts and the static pressure at the slots changes therebyproducing a signal that is dependent on the angular rate of rotation ofthe sensor. The change in the pressure measured at a point on thecylinder with respect to a change in the stagnation point is given bydp/d6=-4pV,, sin 6 cos 9 V,,, the axial velocity of the fluid stream inthe drain, can be calculated approximately by use of the continuityequation if the flow is considered incompressible and isothermal.

The rotation of the rate sensor in a plane perpendicular to its axiscauses the flow to move at an angle a to the axis of the drain. Forsmall deflections, this angle is approximated by tan or a V,V where V isthe average flow velocity in the drain and V, is the tangential velocityat the slots on the pickoff which is found from the law of conservationof angular r= fi ulrr where r, is the radius at the pickoff slot, r,, isthe coupler radius and m is the angular velocity of the sensor. It canbe shown further that rotation of the rate sensor changes the stagnationpoint by the same angle a, which is equivalent to changing the angularposition of the pickoff slot by an angle a.

By way of specific example, two types of slots for the cylindricalpickoff are shown. First, an axial slot such as 22 or 23, which averagesthe radial velocity distribution, and second, a circumferential slotsuch as 28 or 29, shown in FIG. 5, which averages the pressuredistribution around the pickoff 19. The output of the axial slot typepickoff depends on l/r,, where r is the radius of the drain at thepickoff slot. Because of the limit circle at the center of the vortexproduced in the drain, the actual output does not increase as rapidly asmight be expected from a consideration of d p/dw. The output of thecircumferential slot type pickoff depends on sin 20. By averaging thisparameter over the angular length of the slot it can be shown that themaximum output occurs at 45"; therefore, the average slot positionshould be placed at 45 from the stagnation point. In the axial slottedcase, for maximum output, the angular position of the slot is alsoapproximately 45. The circumferential slot should be placed at a smallradius, r so as to obtain a relatively large helical angle.

The size of the pickoff slot is determined by the input impedance of thepure fluid device to be driven by the sensor. If the device has a lowinput impedance, the slots must be large to supply flow. If the deviceon the other hand has a high input impedance, the slots should be smallwhich will give a larger output pressure. The sensor works best withhigh input impedance devices, since the maximum sensitivity occurs forsmall slots. Because averaging over the circumferential slot does notreduce the pressure signal as much as averaging over the axial slot,circumferential slots appear to be better for low impedance devices. Thepresent vortex rate sensor employing slotted cylinder pickoffs forproducing pure fluid output signals can be made a pushpull device byproviding one cylinder per drain in a double drain type rate sensor asmentioned above, with 6 each cylinder having a single slot positioned atthe optimum angle 9 from the stagnation point.

Also, while the cylindrical pickoffs 19 are shown to extend only to thecentral axis AA, cylinder 19 may extend completely across the drainopening 21 along the axis BB shown in FIG. 3. This arrangement producessomewhat less noise and is easier to construct.

To increase the amplitude of the pressure signal produced by acylindrical slotted pickoff, an airfoil section 31 is inserted in drainpassage 21, a short distance upstream of slotted cylinder 19. Airfoilsection 31 is preferably a symmetrical airfoil that possesses a highcoefficient of lift to drag ratio, and is positioned with the chord ofthe airfoil in line with the direction of the drain flow for aparticular initial condition of rotation of the sensor. In mostsituations, the chord of the airfoil section 31 coincides with the drainaxis AA. The angle between the chord of the airfoil section and eitherslot 22 or 23 should equal the optimum angle 6, but it is contemplatedthat this angle can be varied for purposes of biasing the rate sensor.The airfoil section 31 senses a change in the helical angle a of theflow in the drain as a change in angle of attack. When the angle ofattack is not zero, the flow velocity on one side ofthe airfoil isgreater than the flow velocity on the other side of the airfoil. Whenthese flows of different velocities meet at the trailing edge 33 of theairfoil 31, the angle a between the direction of this flow and the drainaxis AA is considerably greater than the angle of attack at the leadingedge 32. Slotted cylinder 19 which extends into the drain passages 21under and along the trailing edge 33 of airfoil 31 sees the change inthis flow direction as a change of angle of attack resulting in adifferential pressure across slots 22 and 23.

The fluid output signal produced by slotted cylinder 19 in combinationwith the symmetrical airfoil section 31 is in the order of ten timesgreater than the fluid output signals produced by the slotted cylinderalone. The reason for the increased sensitivity of this combination isof course that the angle of deflection a in the flow at the trailingedge of airfoil section 31 is greater than the helical angle a of theflow in the drain upstream of the airfoil section. In FIG. 7 airfoilsection 31 is shown to extend half way across drain passage 2l, but itis advantageous in some instances to have airfoil section 31 extendcompletely across the passage. Cylindrical pickoff l9 likewise canextend completely across the passage for the reasons given above.

Because of turbulence that exists along the trailing edge of an airfoilsection caused by vortices generated along this edge, an alternatearrangement is to position the cylindrical pickoff a small horizontaldistance away from axis AA and the chord ofthe airfoil. It is alsocontemplated that an airfoil section such as 31 may be positionedupstream and between a pair of slotted cylinder pickoffs that areseparated from one another a short distance on either side of thecentral axis with the cylinders having only a single slot and one outputchannel each as compared to the double channel output pickoff describedabove.

The vortex rate sensor pickoff techniques disclosed in FIGS. 2 through 7are utilized to produce pressure type output signals with relatively lowflow. When a high flow signal is required that is proportional to theangular rate of rotation of the sensor, the pickoff arrangement shown inFIGS. 8 through 10 is employed.

A symmetrical airfoil section 41 having a high coefficient of lift todrag ratio is installed in the drain 40 of a vortex rate sensortransverse to the drain axis A-A with the chord of the airfoil sectionorientated for a particular drain flow condition but typicallycoinciding with the drain axis AA and extending completely across thedrain opening as more clearly shown in FIG. 9. Airfoil section 41 ispreferably positioned in an expanding portion 42 of the drain 40 foroptimum efficiency. Below the airfoil section 41, or downstream, thedrain becomes four equal output channels 44, 45, 46, and 47 which areformed by a double splitter 43.

When the vortex rate sensor is rotated in a plane perpendicular to itsaxis A-A, a vortex is generated in the chamber (not shown), and ahelical flow is generated in the drain 40. The airfoil section 41 seesthe helical angle a as an angle of attack and when this angle is notzero, the velocity on one side of the airfoil is greater than thevelocity on the other side. At the trailing edge where these two streamsof different velocities meet, a deflection of the drain flow occurs inthe expanded region 42 of the drain 40 which produces a differentialflow across splitter 43. As a result of the deflection of the drain flowcaused by airfoil section 41, a differential flow is produced across thesplitter 43.

Assuming a counterclockwise rotation of the rate sensor as indicated bythe direction of w in FIG. 1, helical flow having a counterclockwisedirection will be produced in drain 40, as shown by the arrow V in FIG.9. This flow will result in the higher velocity flow leaving the outputchannels 45 and 46 and the lower velocity flow leaving the drain viaoutput channels 44 and 47 as shown by the plus and minus signs,respectively, in FIG. 10. The double splitter 43 in dividing the draininto 4 equal output channels provides a dual push-pull output.

The flow output signal produced in the output channels 44 to 47 becomethe input signals for an appropriate pure fluid device (not shown)having a low input impedance. Airfoil section 41 can alternatively beinstalled in drain 40 to extend only as far as the drain axis A-A in acantilevered manner such as in the airfoil and slotted cylinderarrangement shown in FIG. 7. This construction will tend to increase theoutput flow but it will also result in somewhat more noise in the outputsignal.

High flow output signals can also be produced by means of a flow dividerdevice in the drain such as shown in FIGS. 8-10, but not including anairfoil section upstream thereof. A pickoff arrangement without anairfoil section will result in less noise being produced in the outputsignals but will probably sacrifice the sensitivity associated with anairfoil section being present in the drain upstream of the divider. Inthis arrange ment, the sensitivity can be increased to a certain extentby positioning one of the diametrical edges of the double splitter 43 aslight distance upstream of the other.

In the pickoff arrangements employing slotted cylinders as shown inFIGS. 2-7, the openings are positioned in the drain to produce an outputsignal in the form of a pressure change that is proportional to theangular rate of rotation of the sensor. From a consideration of apressure and velocity distribution curve such as shown in FIG. 11, whichis taken for actual vortex flow including viscous effects which were notconsidered in arriving at earlier equations, ofa portion of the fluid inthe region of the drain near r= rotates like a solid body and thetangential velocity V, then varies as the product of rw. Outside thiscentral core of solid body 8 rotation is a transition region. Outsidethe transition region the fluid flows as in a free vortex, wheretangential velocity V, varies as K/r. From the curve shown in FIG. 11,it can be seen that the region of the highest tangential velocity, andconsequently the region of highest pressure, is located in thetransition region.

It, therefore, becomes apparent that the optimum position for theopening in the cylindrical pickoff should be located at a radius r whichcorresponds to the midpoint of the transition region. However, since thetransition region and the radius r are extremely difficult to locate andbecause the opening should be sufficiently large enough to produce ausable output signal, the opening in the cylinder will in most instancesbe large enough to extend across the entire transition region.

In dealing with vortex sink flow as with most any other kind of fluidflow, it is very important that edges and abrupt changes in the shape ofthe walls containing the fluid be avoided to reduce turbulence. For thisreason, the entrance to the drain tube 18 in the vortex rate sensor 10is shown to have a smoothly curved edge 20 to reduce turbulent effectswhich, of course, result in the noise in the output signals from therate sensor.

In one embodiment of [our] my invention, the following dimensions areemployed. The inside diameter of coupler 15 is 3.625 inches. The heightof the chamber is .1 inch. Drain passage 18 has an inside diameter of0.080 inch. Circumferential slots 28 and 29 have a length of 0.010 inch,a width of .008 inch and are located at an average or mean radius r of.005 inch. These dimensions are merely illustrative and [we] I do notwish to be limited thereto.

It will be apparent that the embodiments shown are only exemplary andthat various modifications can be made in construction and arrangementwithin the scope of the invention as defined in the appended claims.

[We] 1 claim as [our] my invention:

1. In a pure fluid device for sensing the angular rate of rotation of abody about an axis including a vortex chamber having a circularcross-sectional area, means for introducing pressurized fluid into saidchamber with substantially only a radial component of velocity and acylindrical drain passage located at the center of said chamber with theaxis of said drain passage coinciding with the axis of said chamber andbeing parallel to the axis of said body, whereby upon rotation of saiddevice in a plane perpendicular to the axis of said body vortex flow isgenerated in said chamber and helical flow is generated through saiddrain passage, improved fluid readout means for said device for sensingchanges in said helical flow as a measure of the rate of rotation ofsaid device comprising:

a. a hollow cylindrical pickoff tube located in said drain passage withthe axis of said pickoff being transverse to said drain axis;

b. a portion of the wall of said pickoff having aperture means forproviding fluid communication be tween said drain passage and outputchannel means in said pickoff;

. said pickoff being orientated in said drain passage with said aperturemeans displaced from the axis of said drain by an angle 0 such that thepressure produced at said aperture means is substantially static;

d. said pickoff producing fluid output signals in response to thechanges in the helical angle of said drain flow as measured bycorresponding changes in the static pressure at said aperture mea ns;

b. whereby the maximum tangential velocity and consequently the highestpressure of said drain flow will be sensed by said pickoff.

3. The rate sensing device according to claim 2 wherein:

a. said aperture means comprises a pair of spaced slots with theirrespective centers being separated from each other in said pickoff wallby an angle equal to 26,

b. each of said slots communicating with a separate output channel insaid pickoff for producing fluid output signals in response to thepressure changes sensed at said slots as the helical angle of said drainflow changes,

0. whereby said fluid output signals are proportional to said rate ofrotation of said drive.

4. The rate sensing device according to claim 3, wherein said slots areparallel to each other and are axially arranged in said pickoff wall.

[5. The rate sensing device according to claim 3, wherein said slots arecircumferentially arranged] 6. The rate sensing device according toclaim 3, wherein the angle 0 equals approximately 45.

[7. In the rate sensing device claim 1, the fluid readout means furthercomprising:

a. an airfoil section located in said drain passage transversely of saiddrain axis with the trailing edge thereof being upstream of and in closeproximity with said pickoff means,

b. said airfoil section being a symmetrical airfoil processing a highcoefficient of lift to drag ratio,

c. said airfoil section cooperating with said pickoff to provide anamplification of the changes in the .helical angle of said drain flow tobe sensed by said pickoff slots,

d. whereby the pressure of said output signals is greatly increased] [8.In the rate sensing device according to claim 3, the fluid readout meansfurther comprising:

a. a symmetrical airfoil section possessing a high coefficient of liftto drag ratio located in said drain passage transversely of said drainaxis with the trailing edge thereof being upstream of and in closeproximity with said pickoff,

b. said airfoil section being positioned between said pickoff slots suchthat the angle between the chord of the airfoil and one of said slots isequal to 6,

c. said airfoil section cooperating with said pickoff to provide anamplification ofthe changes in the helical angle of said drain flow tobe sensed by said pickoff,

d. whereby the sensitivity of said readout means is greatly increased][9. In a vortex angular rate sensor having a vortex chamber suppliedwith fluid under pressure, an input manifold, a porous coupler ring, anda cylindrical drain passage located at the axis of said chamber andwherein the fluid enters said chamber from said manifold through saidring having substantially only a radial component of velocity, wherebyupon rotation of said rate sensor in a plane perpendicular to said axisvortex flow is generated in said chamber and helical flow is generatedthrough said drain, improved readout means for producing fluid outputsignals indicative of the rate of rotation of said device comprising:

a. double splitter means extending across said drain passage anddividing said passage into four equal output channels,

b. the upstream edges of said splitted means being transverse to theaxis of said drain passage,

c. said splitter means producing a differential flow in said outputchannels in response to a change in said helical flow,

d. whereby said differential flow results in a high flow output signalin said output channels that is proportional to the rate of saidrotation,

e. a symmetrical airfoil section possessing a high lift to drag ratiopositioned in an expanded portion of said drain passage upstream of saidsplitter means,

f. said airfoil section being transverse to the axis of said passage,

g. said airfoil section cooperating with said splitter means to deflectsaid helical drain flow to produce a differential flow across saidsplitter means,

h. whereby said differential flow generates high flow output signals insaid output channels proportional to the rate of said rotation] [10. Therate sensor according to claim 9, wherein the edge of one portion ofsaid splitter means that ex tends diametrically across said drainpassage is located a slight distance upstream of the other edge portion01 said splitter means whereby the sensitivity of said readout means isimproved] II. .4 sensor for providing afluid pressure signal as afunction of the vortical fluid flow component of combined axial andvorticalfluidflow in a fluidflow channe. having a specified centrallongitudinal axis, said sensor comprising: a hollow body having aninterior chamber said hollow body being positioned in said channel intht path ofsaid combinedfluidflow, a sensor orifice define: in saidhollow body for providing fluid communicatior between said channel andsaid interior chamber, said sen sor orifice being directed generallytoward said combiner fluid flow and displaced from said centrallongitudina axis whereby to sense the angle ofattack ofsaid vertica flowand thereby generate a fluid pressure in said cham ber proportional tosaid vertical fluid flow.

12. The combination according to claim 11 whereit said hollow body is acylinder disposed transversely o said combined fluid flow.

1. In a pure fluid device for sensing the angular rate of rotation of abody about an axis including a vortex chamber having a circularcross-sectional area, means for introducing pressurized fluid into saidchamber with substantially only a radial component of velocity and acylindrical drain passage located at the center of said chamber with theaxis of said drain passage coinciding with the axis of said chamber andbeing parallel to the axis of said body, whereby upon rotation of saiddevice in a plane perpendicular to the axis of said body vortex flow isgenerated in said chamber and helical flow is generated through saiddrain passage, improved fluid readout means for said device for sensingchanges in said helical flow as a measure of the rate of rotation ofsaid device comprising: a. a hollow cylindrical pickoff tube located insaid drain passage with the axis of said pickoff being transverse tosaid drain axis; b. a portion of the wall of said pickoff havingaperture means for providing fluid communication between said drainpassage and output channel means in said pickoff; c. said pickoff beingorientated in said drain passage with said aperture means displaced fromthe axis of said drain by an angle theta such that the pressure producedat said aperture means is substantially static; d. said pickoffproducing fluid output signals in response to the changes in the helicalangle of said drain flow as measured by corresponding changes in thestatic pressure at said aperture means; e. whereby said fluid outputsignals are proportional to the angular rate of said rotation.
 2. Therate sensing device according to claim 1 wherein: a. the center of saidaperture means is located closely adjacent to said drain axis in thevicinity of the radius of the limit circle in the transition region ofsaid helical flow produced in said drain, b. whereby the maximumtangential velocity and consequently the highest pressure of said drainflow will be sensed by said pickoff.
 3. The rate sensing deviceaccording to claim 2 wherein: a. said aperture means comprises a pair ofspaced slots with their respective centers being separated from eachother in said pickoff wall by an angle equal to 2 theta , b. each ofsaid slots communicating with a separate output channel in said pickofffor producing fluid output signals in response to the pressure changessensed at said slots as the helical angle of said drain flow changes, c.whereby said fluid output signals are proportional to said rate ofrotation of said drive.
 4. The rate sensing device according to claim 3,wherein said slots are parallel to each other and are axially arrangedin said pickoff wall.
 6. The rate sensing device according to claim 3,wherein the angle theta equaLs approximately 45*.
 11. A sensor forproviding a fluid pressure signal as a function of the vortical fluidflow component of combined axial and vortical fluid flow in a fluid flowchannel having a specified central longitudinal axis, said sensorcomprising: a hollow body having an interior chamber, said hollow bodybeing positioned in said channel in the path of said combined fluidflow, a sensor orifice defined in said hollow body for providing fluidcommunication between said channel and said interior chamber, saidsensor orifice being directed generally toward said combineD fluid flowand displaced from said central longitudinal axis whereby to sense theangle of attack of said vertical flow and thereby generate a fluidpressure in said chamber proportional to said vertical fluid flow. 12.The combination according to claim 11 wherein said hollow body is acylinder disposed transversely of said combined fluid flow.